1. Field of the Invention
This invention relates generally to an ophthalmic lens, and more specifically to an ophthalmic lens having coupled thereto or integrated thereon one or more rotationally asymmetric and/or non-continuous diffractive zones for varying phase delay in order to improve vision at a range of distances, as well as systems and methods relating to same.
2. Description of the Related Art
Surgery on the human eye has become commonplace in recent years. Many patients pursue eye surgery as an elective procedure, such as to avoid the use of contacts or glasses. Other patients pursue surgery to correct an adverse condition in the eye. Such adverse conditions may include, for example, cataracts or presbyopia, as well as other conditions known to those skilled in the art.
The anatomy and physiology of the human eye is well understood. Generally speaking, the structure of the human eye includes an outer layer formed of two parts, namely the cornea and the sclera. The middle layer of the eye includes the iris, the choroid, and the ciliary body. The inner layer of the eye includes the retina. The eye also includes, physically associated with the middle layer, a crystalline lens that is contained within an elastic capsule, also referred to as the lens capsule, or capsular bag. Image formation in the eye occurs by entry of image-forming light to the eye through the cornea, and refraction by the cornea and the crystalline lens to focus the image-forming light on the retina. The retina provides the light sensitive tissue of the eye.
Ophthalmic lenses, such as intraocular lenses (IOLs), phakic IOLs and corneal implants may be used to enhance or correct vision, such as to correct for the aforementioned adverse conditions, including aberrations or inadequacies that adversely affect the performance of the referenced structures of the eye. For example, IOLs are routinely used to replace the crystalline lens of an eye that is removed during cataract surgery.
Ophthalmic lenses, such as IOLs, may be monofocal, multifocal, or may include monofocal and multifocal portions. More particularly, a monofocal IOL portion may provide a single focal point, whereas a multifocal IOL portion may provide multiple focal points, such as for correction of vision at different distances. For example, a bifocal IOL may provide two different focal points, typically for near and distant vision.
A diffractive bifocal IOL may divide incident light into two diffractive orders to provide the aforementioned near and distant bifocal vision. In such lenses, the optic area is generally divided into a plurality of echelettes that are offset parallel to the optical axis by predetermined diffractive step heights in order to provide a specific phase relationship.
A phase “plate” is typically comprised of a plurality of echelettes in which the optical height of the steps causes a phase delay. For example, a step height of one-half times the design wavelength results in approximately 80% of the light at the design wavelength being evenly split between zeroeth and first diffraction orders. This phase plate configuration may be used to produce a bifocal lens in which the zeroeth diffraction order produces a first focal point for distant vision, and the first diffraction order produces a second focal point corresponding to near or intermediate vision. A step height equal to the design wavelength results in a monofocal diffractive IOL that may be used to correct for chromatic aberration.
A first particular problem associated with diffractive multifocal/bifocal IOLs is dysphotopsia, i.e. halos and glare. Halos arise when light from the unused focal image creates an out-of-focus image that is superimposed on the used focal image. For example, if light from a distant point source is imaged onto the retina by the distant focus of a bifocal IOL, the near focus of the IOL will simultaneously superimpose a defocused image on top of the image formed by the distant focus. This defocused image may manifest itself in the form of a ring of light surrounding the in-focus image, referred to as a halo. A second problem frequently associated with diffractive multifocal/bifocal IOLs is reduced contrast vision. These difficulties arise, at least in part, due to the symmetric, and/or the concentric, nature of the aforementioned diffractive echelettes of the IOL.
Thus, a need exists for a lens, system and method that improves the performance of multifocal lenses, and particularly of multifocal ophthalmic lenses.